The present invention relates to a control device for an electronic timepiece, and in particular to a control device for controlling a stepping motor used in an electronic timepiece which uses kinetic energy to drive a electricity generating device to provide electronic power for driving the stepping motor.
In recent years, timing devices, such as wrist-watches, have been sold with built-in electricity generators in which the energy generated by the movement of the user's arm is converted into electricity which is used to drive the stepping motor which moves the hands of the device. These timing devices operate without batteries and can continuously run off the energy generated by the user's movement. Also, these timing devices eliminate the often cumbersome process of changing batteries as well as help reduce the environmental hazard associated with battery disposal. As a result, built-in electricity generators are being closely evaluated for future widespread use in wristwatches and similar devices.
Generally, electronic timepieces that incorporate electricity generators include a stepping motor for driving the hands of the timepiece. These stepping motors, also referred to as a pulse motors or digital motors, are driven by pulse signals and are also extensively used as actuators for digital control devices. In recent years, compact electronic devices and information equipment have been developed in which portability is desirable, and compact and lightweight stepping motors are in widespread use as actuators for this equipment. Representative of such electronic devices are timing devices including electronic timepieces, time switches and chronographs.
Referring now to FIG. 12, there is shown a prior art timing device 9, for example a wristwatch, which includes a stepping motor 10, a driving circuit 30 for driving stepping motor 10, a gear train 50 for transferring the force of stepping motor 10, a second hand 61, a minute hand 62, and an hour hand 63 which are moved by gear train 50. Stepping motor 10 generates magnetic force in response to driving pulses supplied from a control device 20. Stepping motor 10 includes a driving coil 11, a stator 12 which is excited by driving coil 11, and a rotor 13 which rotates within stator 12 as a result of the excited magnetic field. By selecting a disk-shaped bipolar permanent magnet for rotor 13, a PM-type (Permanent Magnet rotational) stepping motor is formed. Stator 12 is provided with a magnetism saturating unit 17 so that the different magnetic poles that result from the magnetic force generated by driving coil 11 are generated at the phases (poles) 15 and 16, respectively surrounding rotor 13. Also, an internal notching 18 is provided at the appropriate location on the inner periphery of stator 12 so that cogging torque is generated and rotor 13 is stopped at the appropriate position.
The rotation of rotor 13 of stepping motor 10 is transferred to each of the timepiece hands by gear train 50 which includes a fifth gear 51 meshing with a fourth gear 52, which also meshes with a third gear 53, which meshes with a center wheel 54. Center wheel 54 meshes with a minute wheel 55, which meshes with an hour wheel 56. Second hand 61 is connected to the axis of fourth gear 52, minute hand 62 is connected to the axis of center wheel 54, and hour hand 63 is connected to the axis of hour wheel 56. Time is displayed by each of the timepiece hands operating synchronously with the rotation of rotor 13. Of course, a transfer system for displaying the year, month, and day (not shown) may also be connected to gear train 50. In order for timing device 9 to display the time as a result of the rotation of stepping motor 10, stepping motor 10 is supplied with driving pulses which are based on counting (timing) of signals generated by a reference frequency.
Control device 20, which controls stepping motor 10, includes a pulse synthesizing circuit 22 for generating reference pulses of a standard frequency using a reference oscillator 21 such as a crystal oscillator, or pulse signals of a different pulse width or timing. The reference pulses are input to a control circuit 23 for controlling stepping motor 10 based on the various pulse signals supplied from pulse synthesizing circuit 22. Control circuit 23 has a driving control circuit 24 which receives the reference pulses for controlling driving circuit 30, and a detecting circuit 25 for detecting whether driving rotor 13 rotated. Driving control circuit 24 includes: a driving pulse supplying unit 24a for supplying driving pulses to driving circuit 30 which in turn drives driving rotor 13 of stepping motor 10; a rotation detection pulse supplying unit 24b for outputting rotation detecting pulses to detection circuit 25 for inducing induction voltage to determine whether driving rotor 13 rotated in response to the driving pulse; a magnetic detection pulse supplying unit 24c for outputting magnetic field detecting pulses to detection circuit 25 prior to the output of the driving pulse, for inducing induction voltage to detect the presence of a magnetic field external to stepping motor 10; an auxiliary pulse supplying unit 24d for generating an auxiliary pulse that has an effective electric power that is greater than that of the driving pulse, the auxiliary pulse being output if the driving pulse does not cause driving rotor 13 to rotate or if an external magnetic field has been detected; and a demagnetizing pulse supplying unit 24e for producing a demagnetizing pulse having a polarity that is opposite that of the auxiliary pulse and which is used to demagnetize driving coil 11 after the auxiliary pulse is output.
Detecting circuit 25 includes a rotating detecting unit 26 for comparing the rotation detecting induction voltage, obtained by outputting the rotation detecting pulse, with a set value, and detecting whether driving rotor 13 rotated. Detecting circuit 25 also includes a magnetic field detecting unit 27 for comparing the magnetic field detecting induction voltage, obtained by outputting the magnetic field detecting pulse, with a set value for detecting the presence of a magnetic field.
Referring now to FIG. 13, there is shown rotation detecting unit 26 which employs a pair of comparators, 29a and 29b, to compare the value of the bi-directional excitation voltage generated in driving coil 11 with a set value SV1, to determine whether driving rotor 13 has rotated. Comparator 29a receives one input from the standard signal SV1 and a second input .phi.1 from one side of driving coil 11 and produces a first comparison signal. Similarly, comparator 29b receives a first input SV1 and a second input .phi.2 from the other side of driving coil 11 and produces a second comparison signal. An OR gate 29c receives the first and second comparison signals and produces an output to driving control circuit 24. Similarly, magnetic field detecting unit 27 uses a pair of inverters, 28a and 28b, each having a threshold value of SV2, which receive the inputs of .phi.1 and .phi.2, respectively. These inverted signals are input to an OR gate 28c for detecting the presence of a magnetic field. The results of each comparison are fed back to driving control circuit 24, and are used for controlling stepping motor 10.
Driving circuit 30, which supplies various driving pulses to stepping motor 10 under the control of driving control circuit 24, coupled between driving control circuit 24 and a battery 41, has a bridge circuit which includes a serially connected p-channel MOSFET 33a and n-channel MOSFET 32b, and serially connected p-channel MOSFET 33b and n-channel MOSFET 32a, configured for controlling the voltage supplied to stepping motor 10 from battery 41. Also included are a pair of rotation detecting resistors 35a and 35b connected in parallel to the p-channel MOSFET 33a and 33b, respectively, and a pair of sampling p-channel MOSFET, 34a and 34b, coupled between ground, driving circuit 24 and resistors 35a, 35b respectively for supplying chopper pulses to resistors 34a and 35b. Control pulses having different polarities and pulse widths are output from supplying unit 24a through 24e of driving control circuit 24 to the gate electrodes of each of MOSFET 32a, 32b, 33a, 33b, 34a and 34b according to the respective timings. Thus, driving pulses having different polarities drive driving coil 11 and pulses for inducing induction voltage for rotation detection of rotor 13 and magnetic field detection are supplied.
Referring now to FIG. 14, there is shown a timing chart illustrating the control signals supplied to gates GP1, GN1, and GS1 of the p-channel MOSFET 33a, n-channel MOSFET 32a, and sampling p-channel MOSFET 34a, respectively, for excitation of a magnetic field of one polarity across driving coil 11, and to gates GP2, GN2 and GS2 of the p-channel MOSFET 33b, n-channel MOSFET 32b, and sampling p-channel MOSFET 34b, respectively, for excitation of a magnetic field of a reverse polarity across driving coil 11. Control device 20 controls the movement of the timepiece hands each second, by supplying a series of control pulses to driving circuit 30 which in turn controls stepping motor 10. At the beginning of a timing cycle, pulses SP0 and SP1 are output from driving control circuit 24 for detecting whether a magnetic field is present which causes rotation detection to be unreliable. Pulse SP0, which is output at the time t1, is used for detecting the presence of a magnetic field due to high-frequency noise. The control signals for outputting magnetic field detecting pulse SP0 are supplied by magnetic field detecting pulse supplying unit 24c to gate GP1 of the p-channel MOSFET 33a on the driving side (driving pole side) i.e. the side of driving circuit 30 from which driving pulse P1 is output. Magnetic field detecting pulse SP0 is a continuous control pulse having a pulse width of approximately 20 ms and is used to detect magnetic noise caused by, for example, the switching of household electrical appliances such as electric blankets or infrared foot-warmer tables. After pulse SP0 is output, a control signal for outputting a magnetic field detecting pulse SP1 for detecting alternating current magnetic fields of 50 to 60 Hz is output at time t2 by magnetic detecting pulse supplying unit 24c to gate GP2 of p-channel MOSFET 33b on the side that is opposite to the driving pole side (i.e. reverse pole). Magnetic field detecting pulse SP1 is an intermittent chopper pulse having a duty ratio of approximately 1/8, and samples the electric current induced in driving coil 11 by the alternating current magnetic field thus enabling magnetic field detection unit 27 of detecting circuit 25 to detect the presence of a magnetic field. Also, because the magnetic field detecting capabilities of the driving side, i.e., the p-channel MOSFET 33a and the n-channel MOSFET 32a, deteriorates after an auxiliary pulse is applied, control pulse SP1 is output to gate GP2 of p-channel MOSFET 33b which is at the opposite pole of the driving side (reverse pole). Such magnetic field detection is disclosed in detail in Japanese Examined Patent Publication No. 3-45798.
After magnetic field detecting pulses SP0 and SP1 are output, control pulses for outputting driving pulse P1 at time t3 is supplied by driving pulse supplying unit 24a to gate GN1 of the n-channel MOSFET 32a and gate GP1 of the p-channel MOSFET 33a of the driving pole side. The effective electric power of the driving pulse P1 is reduced to approximately the limit of rotation of driving rotor 13, and is selected such that driving pulse P1 has pulse width of, e.g. W10. The control signal for outputting driving pulse P1 can vary the pulse width of driving pulse P1 thereby controlling the effective electric power of driving pulse P1. If driving rotor 13 does not rotate in response to driving pulse P1 and it is therefore necessary to output auxiliary pulse P2 to rotate driving rotor 13, the pulse width of driving pulse P1 is widened thereby increasing its effective electric power. On the other hand, if rotor 13 is continuously driven for a predetermined number of times by driving pulses P1 having the same pulse width, the effective electric power of driving pulse P1 can be reduced by narrowing its pulse width.
After driving pulse P1 is output, rotation detection pulse supplying unit 24b outputs a rotation detection pulse SP2 to gate GP1 of the p-channel MOSFET 33a on the driving side and to sampling p-channel MOSFET 34a at time t4 for detecting whether rotor 13 rotated. Rotation detecting pulse SP2 is a chopper pulse with a duty ration having approximately 1/2, and causes the induction electric current induced in driving coil when rotor 13 rotates to be output to rotation detecting resister 35a. The voltage across rotation detecting resister 35a is compared by rotation detecting unit 26 of detecting circuit 25 with a set value SV1 for determining whether driving rotor 13 has rotated.
If the induction voltage induced by rotation detecting pulse SP2 is not at least set value SV1, it is determined that rotor 13 did not rotate, and a control signal for outputting auxiliary pulse P2 at time t5 is output from auxiliary pulse supplying unit 24d to gate GP1 of n-channel MOSFET 32a on the driving side and also to gate GP1 of p-channel MOSFET 33a. Auxiliary pulse P2 has a width of W20 and has a greater effective electric power than driving pulse P1. Thus, auxiliary pulse P2 has sufficient energy to ensure that rotor 13 rotates. Auxiliary pulse P2 is output instead of driving pulse P1 when the rotation of rotor 13 is not detected and when a magnetic field is detected by either of magnetic field detecting pulses SP0 and SP1. If a magnetic noise is present in the area of stepping motor 10, it is possible that rotation detecting pulse SP2 falsely detects the rotation of rotor 13 thereby causing errors in the movement of the timepiece hands. Accordingly, if a magnetic field is detected, an unnecessary auxiliary pulse P2 is output for detecting rotation, which while increasing power consumption, will prevent errors in the movement of the timepiece hands.
If auxiliary pulse P2 is output, a control pulse for outputting a demagnetizing pulse PE at time t6 is supplied by the demagnetizing pulse supplying unit 24e to gate GN2 of n-channel MOSFET 32b, which is at the reverse pole, and to gate GP2 of the p-channel MOSFET 33b. Demagnetizing pulse PE, a pulse which is of reverse polarity to auxiliary pulse P2, reduces the residual magnetic flux of driving coil 11 which is generated by the high effective electric power of auxiliary pulse P2. After demagnetizing pulse PE is output, one cycle of the rotational driving of stepping motor 10 by one step angle is completed.
One second after time t1, the next cycle of rotational driving of stepping motor 10 by one step angle starts at t11. In this cycle, MOSFET 32b, 33b, and 34b which were on the reverse side in the previous cycle now become the driving pole side. As with the previous cycle, pulse SP0 is first output at time t11 for detecting magnetic flux noise due to high-frequency noise, and then pulse SP1 is output at time t12 for detecting noise due to a low-frequency alternating current magnetic field. If magnetic noise is not detected, driving pulse P1 is output at time t13. Because auxiliary pulse P2 has been output in the previous cycle, the effective electric power of driving pulse P1 is increased, and a driving pulse P1 a width W11 (where W11&gt;W10) is output at time t13. Next, rotation detecting pulse SP2 is output at time t14, and if rotation of rotor 13 is detected, the cycle ends.
Referring now to FIG. 15, there is shown a flow chart of the above-described operation of control device 20. First, in step ST1, a timing reference pulse is counted and a one second time duration is measured. If it is determined that one second elapses, then in step ST2, a high-frequency magnetic field is detected using magnetic field detecting pulse SP0. If a high-frequency magnetic field is detected, then, in step ST7, auxiliary pulse P2 having a greater effective electric power than driving pulse P1 is output instead of the driving pulse P1, thus preventing errors in the movement of the timepiece hands from occurring due to unreliable rotation detection. If a high-frequency magnetic field is not detected, in step ST3, the presence of an alternating current magnetic field of a low-frequency is detected in steps using magnetic field detecting pulse SP1. If an alternating current magnetic field is present, then in step ST7, auxiliary pulse P2 is output thus preventing errors in the movement of the timepiece hands from occurring.
If no magnetic field is detected in any steps ST2, ST3, then in step ST4, driving pulse P1 is output and, in step ST5 it is determined whether rotor 13 has rotated by output of rotation detecting pulse SP2. If the rotation of rotor 13 is not confirmed, then in step ST7, auxiliary pulse P2 having a greater effective electric power than driving pulse P1 is output thereby ensuring that rotor 13 is rotated. After auxiliary pulse P2 is output, in step ST8, demagnetizing pulse PE is output, and in step ST10, the level of driving pulse P1 is adjusted higher (first level adjustment). If rotation was not confirmed in step ST5, using driving pulse P1 with the same effective electric power will result in the defective rotation being repeated. Accordingly, in step ST11, the cause for the defective rotation which made the output of auxiliary pulse P2 necessary is determined and, in step ST12, the output of driving pulse P1 is set to a higher voltage level to avoid repeated defective rotation in the next cycles. The system then returns to step ST1.
If, in step ST5, the rotation of rotor 13 as a result of driving pulse P1 was detected, the effective electric power of driving pulse P1 is adjusted lower in step ST6 (second level adjustment). In many cases, the effective electric power of driving pulse P1 is reduced after it is confirmed several times that rotor 13 has rotated in response to driving pulse P1. By performing such control, the power consumption of pulse P1 is reduced, and error in the movement of the timepiece hands is prevented from occurring in areas where there are magnetic fields from electric and electronic appliances. Accordingly, a timing device with high reliability and low power consumption is realized.
When an electricity generating device, which converts energy from the movement of the user into electricity, is added to the timepiece, another generator that has a similar configuration as that of stepping motor 10 is introduced. The electricity generating device includes a generating rotor that rotates within a stator, the generating rotor rotates by way of an energy transferring device, such as a rotating weight, thereby changing kinetic energy into rotational energy.
However, the magnetic flux generated by the generator also generates noise that may interfere with the rotation detection of driving rotor 13 thereby lowering the reliability and accuracy of timing device 9. The noise from the generator has a frequency approximately in the range of 200 to 300 Hz and is not easily detected by magnetic field detecting pulse SP0, which is normally designed to detect high frequency noise, or magnetic field detecting pulse SP1, which is used to detect alternating magnetic flux in the 50 to 60 Hz. Furthermore, the generator only generates electricity when the rotating weight rotates due to the user's arm movement. Accordingly, the magnetic field generated by the generator is irregular, and often only e.g., 100 ms. Therefore, it is likely that this noise may be generated at the same time that rotation detecting pulse SP2 is being output even if pulse SP0 or pulse SP1 did not previously detect the presence of magnetic flux. Also, because half-wave rectification, which requires minimal space and is inexpensive to implement, is generally used in electronic timepieces, the magnetic noise is directional. Thus, there is no guarantee that when using the conventional detection system, the presence of magnetic noise will not cause the rotation of rotor 13 to be falsely detected. Furthermore, even if magnetic noise is detected and auxiliary pulse P2, having a greater effective electric power, is output, the magnetic detection capabilities in the same direction will deteriorate due to effects of residual magnetism.
Thus, in order to achieve a highly reliable timing device, it is necessary that control devices for stepping motors built in to timing devices along with alternating current electricity generating devices be provided so that the magnetic field generated by the generating device can be eliminated.